1. Field of the Invention
The present invention is generally related to a method and apparatus for controlling the power output of a homogeneous charge internal combustion engine and, more particularly, to a method and apparatus for controlling a skip charge firing technique relating to an engine with a manual throttle control mechanism.
2. Description of the Prior Art
Many types of skip fire techniques are known to those skilled in the art. For example, U.S. Pat. No. 5,553,575, which issued to Beck et al on Sep. 10, 1996, describes a Lambda control by skip fire of unthrottled gas fueled engines. The performance of a gas-fueled unthrottled internal combustion engine is improved by optimizing excess air ratio in the engine. Lambda (air ratio) is optimized by selecting automatically and continuously the optimum fraction of cylinders firing as a function of engine operating parameters, eliminating the fuel charge from one or more cylinders to obtain firing in the optimum fraction of cylinders firing, and distributing unused fuel to the optimum fraction of cylinders firing, thereby decreasing lambda in the firing cylinders to an optimum level. The optimum fraction of cylinders firing may be calculated according to mathematically derived and empirically weighted equations, or obtained with reference to suitable look-up tables. In addition, optimum lambda and optimum fraction of cylinders firing may be adjusted to take into account the effects of exhaust gas recirculation, engine speed, and/or engine timing. Further lambda adjustment can be performed by suitable control of exhaust gas recirculation, ignition timing, and/or turbo air bypass.
U.S. Pat. No. 5,778,858, which issued to Garabedian on Jul. 14, 1998, describes a fuel injection split engine. An automobile includes an engine and an engine controller. The engine includes multiply cylinders. Each cylinder has a fuel injector connected to the engine controller. The engine controller has a first output which activates a first fraction of the fuel injectors. In addition, the engine controller has a second output which activates a second fraction of the fuel injectors. The engine controller also as an input which provides a timing signal synchronous with rotation of the engine and a sequencing circuit responsive to the timing signal. The sequencing circuit periodically alternates between the first and second output in synchronization with the rotation of the engine.
U.S. Pat. No. 5,377,631, which issued to Schechter on Jan. 3, 1995, describes a skip cycle strategy for four cycle engines. Strategies for operating a four cycle engine in skip cycle manner include providing the engine with a valve control so that each intake and exhaust valve for each cylinder can be individually activated or deactivated essentially instantaneously to provide a skip cycle pattern that varies as a function of a load. Individual ones of the valves permit changing the purpose of the stroke off each piston of each deactivated cylinder for compression to exhaust or intake to expansion, as the case may be to assure firing of all of the engine cylinders within as short a period as one skip cycle to prevent cylinder cooldown, which promotes emissions. Unthrottled operation also is provided by closing the intake and exhaust valves in a particular sequence during skip cycle operation, and controlling the intake valve closure time during load periods between skip cycle periods to continue unthrottled operation for all load levels. Further individual activation or deactivation of the fuel injectors and spark plugs enhances the skip cycle, unthrottled operation.
U.S. Pat. No. 5,826,563, which issued to Patel et al on Oct. 27, 1998, describes a diesel engine cylinder skip firing system. A high horsepower diesel engine is operated in a skip firing mode in which the engine includes a plurality of individually controllable, fuel injected cylinders. The system senses that the engine is operating in a low horsepower mode and has a low fuel demand and therefore selects a firing pattern of cylinders to be fired during each revolution of the engine crankshaft based upon the values of the sensed fuel demand and engine horsepower. The pattern selected for firing the cylinders is arranged such that all cylinders of the engine are fired within a preselected number of crankshaft rotations. The system also senses the engine air-fuel ratio and adjusts the pattern of cylinders being fired so as to maintain exhaust emissions below a preselected level. Additionally, the pattern of fired cylinders may be adjusted to maintain engine operating temperature and as a function of engine speed.
U.S. Pat. No. 4,550,703, which issued to Ootuka et al on Nov. 5, 1985, describes a continuous method of fuel injection in electronically controlled engines. The minimum fuel injection time is on electronically controlled fuel injection engines and is set in relation to the running condition of the engine. For example, in shift change, when the throttle valve is in the idling angle and the revolution speed of the engine is high, the minimum fuel injection time is set to a small value to improve the efficiency of fuel consumption. Also, at the completion of fuel cut-off when the revolution speed of the engine is low, the minimum fuel injection time is set to a large value to improve the driveability of the vehicle.
U.S. Pat. No. 6,273,771, which issued to Buckley et al on Aug. 14, 2001, describes a control system for a marine vessel. The control system incorporates a marine propulsion system that can be attached to a marine vessel and connected in signal communication with a serial communication bus and a controller. A plurality of input devices and output devices are also connected in signal communication with a communication bus and a bus access manager, such as CAN Kingdom network, is connected in signal communication with the controller to regulate the incorporation of additional devices to the plurality of devices in signal communication with the bus whereby the controller is connected in signal communication with each of the plurality of devices on the communication bus. The input and output devices can each transmit messages to the serial communication bus for receipt by other devices.
The patents described above are hereby explicitly incorporated by reference in the description of the present invention.
Many situations can occur, particularly with regard to a marine propulsion system, wherein it is desirable to control the power output of an internal combustion engine independently of an operator controlled manual throttle control mechanism. For example, certain control systems monitor engine temperature and coolant flow and, if engine temperature is above allowable limits, it is desirable to limit the output power of the engine regardless of the control input received from a manually controlled throttle mechanism. Furthermore, during deceleration of a marine vessel propulsion system, it is often desirable to control the rate of deceleration within preselected magnitudes. Furthermore, it is often desirable to limit boat speed and engine speed independently from the input received from a manually controllable throttle mechanism.
If an internal combustion engine is operating in a stratified combustion mode, such as is the case with a direct fuel injected (DFI) fuel system, or makes use of an electronic throttle, engine speed control is easily accomplished. However, with an engine that is operating under a manual throttle control system and incorporates a homogeneous charge combustion mode, engine speed control is not easily accomplished independently from the manual throttle mechanism.
It would therefore be significantly beneficial if a system could be provided in which an internal combustion engine operating with a homogeneous charge could be controlled, with regard to power output, independently of a manual throttle control mechanism.
A method for controlling the power output of a homogenous charge internal combustion engine with a manual throttle control, within the scope of the present invention, comprises the steps of storing a plurality of sets of numerical values, determining a desired power output of the engine, measuring an actual power output of the engine, comparing the desired power output with the actual power output, selecting a selected one of the plurality of sets of numerical values, and selectively activating and deactivating each of a plurality of cylinders of the engine as a function of the selected one of the plurality of sets of numerical values.
Each set of numerical values is associated with a desired power output magnitude of the engine. Each set of numerical values comprises a plurality of numerical values, wherein each of the plurality of numerical values within each of the plurality of sets is associated with a specific one of a plurality of cylinders of the engine.
The selection of the selected one of the plurality of sets of numerical values is based on the relative magnitudes of the desired and actual power outputs, in a preferred embodiment of the present invention. The cylinders can be activated and deactivated by energizing and de-energizing either a spark plug associated with each cylinder or a fuel injector associated with each cylinder, or both.
The numerical values in each of the plurality of sets of numerical values each represent a number of consecutive firing cycles to be executed for an associated cylinder before a skip fire event occurs for that associated cylinder. The comparing and selecting steps can be performed by a proportional-integral-differential (PID) controller or other set-point controller.
In a particularly preferred embodiment of the present invention, the homogeneous charge internal combustion engine is a two cycle engine connected in torque transmitting association with a marine propulsion system. The homogeneous charge internal combustion engine can be a fuel injected engine.